Period? Or implantation?

I got my "period" two days early and i had bad cramps but I've never really had cramps so I don't know if they were really that bad and lower back pain for a couple hours and I spotted first and then I was bleeding a lot but it was very thin and red ish and there was clots and then the next day I just had some pink ish red thin blood but not much and barely any cramps and then yesterday the blood was brown and barely there I took two pregnancy tests the day after the bleeding started and they were negative but the bleeding stopped after three days and it would come and go throughout each day and this is nothing like my period it's normally 5 or more days and very heavy for the first two-three days and I don't get cramps.. Anyone have any ideas?